Optical sample analysis system

Abstract

The invention relates to a method for the optical analysis of a sample in a droplet actuation device operating by electrowetting, said actuation device comprising: A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a principal axis, A first light source (S1) capable of generating said first light beam (L1) directed towards a photoconductive layer (C30) of the lower substrate (101), The upper substrate (100) comprising a second electrode, An optical sample analysis device comprising a second excitation light source (S2) positioned above the upper substrate (100), capable of generating a second light beam (L2) at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate (100) caused by its excitation. Figure to be published with the abbreviation: Figure 2A

Description

Title of the invention: System for optical analysis of a sample Technical field of the invention

[0001] The present invention relates to a system for optical analysis of a sample, comprising in particular a drop actuation device operating by electrowetting. State of the art

[0002] It is known to want to analyze cells or molecules by isolating them in drops. Some drops then constitute micro-reactors and it is thus possible to quickly scan a set of drops to detect and isolate those in which a reaction takes place. Thus, it is easy to isolate cells which may be of interest, for example, for the bio-production of therapeutic molecules.

[0003] However, it is necessary to be able to sort the drops of interest from a set of several drops.

[0004] To manipulate drops and move them, it is known to use the principle of electrowetting (EWOD in English for "Electowetting-on-dielectric"). It makes it possible to move drops by activating electrodes between two substrates. The forces used are electrostatic forces. Patent application FR2841063A1 describes in particular this principle which uses a catenary placed opposite several juxtaposed electrodes. The electrodes are activated individually to move the drop along the catenary. Patent application WO2006 / 070162A1 also describes a drop dispensing device using this electrowetting principle to move the drops.

[0005] An alternative embodiment of a sorting device operating by electrowetting consists of creating a matrix of virtual electrodes, according to the principle called "Opto-EWOD" and described in the publication referenced PY Chiou, H. Moon, H. Toshiyoshi, CJ Kim, and MC Wu, “Light actuation of liquid by optoelectrowetting,” Sensors Actuators, A Phys., vol. 104, no. 3, pp. 222-228, 2003.

[0006] In this variant, one of the two substrates used comprises a stack of layers, including an unstructured photoconductive layer. Light radiation makes it possible to locally make the photoconductive layer conductive, defining a virtual electrode both temporally and locally. The light beam therefore locally induces the electrowetting effect on the scale of a droplet without having to manufacture a matrix of electrodes on the surface of the substrate where the drops rest. This results in a matrix of virtual electrodes generated by light. The light source used must allow the formation of images, or at least localized illumination on short durations. The type of technology that can meet these requirements can be a laser source that scans the surface of the electrowetting in order to activate the drops on the surface, a screen type solution whether emissive (OLED, LED, ...), transmissive (LCD) or even projection (video projector).

[0007] This principle is taken up in patent application WO2023 / 281274A1. It is implemented in conjunction with a device for optical analysis of drops. In other words, electrowetting according to the "opto-EWOD" principle is used to precisely fix a drop between two substrates and an optical analysis (for example by fluorescence) is carried out on the drop using an excitation light source and a detector. This patent application is more particularly interested in the problem linked to the disturbances caused by the excitation light source on the light source used for electrowetting, and vice versa. In other words, it is possible that the excitation light source also excites the photoconductive layer, which can cause disturbances in the fixing of the drop between the two substrates.

[0008] In addition, the light source required to activate the opto-EWOD may generate additional light that interferes with the optical analysis of the drop. All of this makes it difficult to optically analyze a drop and actuate it by "opto-EWOD" simultaneously.

[0009] To remedy this, it is proposed in patent application WO2023 / 281274A1 to activate the excitation light source used for optical analysis, only when the electrostatic field is deactivated, i.e. when the electrowetting system is inactive.

[0010] This prior solution does not, however, allow continuous analysis of the drops trapped in the system. It also requires fine adjustment of the periods of activation and deactivation of the electrostatic field. During a period of deactivation of the electrostatic field, it is also possible for the drops to move between the two substrates, which can cause errors in the optical analysis.

[0011] The aim of the invention is to propose a system for optical analysis of a liquid sample, which uses the principle of electrowetting of the "opto-EWOD" type and which is capable of overcoming the drawbacks of the state of the art. Statement of the invention

[0012] This aim is achieved by a method of optical analysis of a sample in a drop actuation device operating by electrowetting, said actuation device comprising: - A chamber formed by two substrates arranged opposite each other along a main axis, so as to form a so-called lower substrate and a so-called upper substrate. upper, the two substrates being spaced from each other to form a space for receiving said sample, - The lower substrate being produced by a stack of layers in which a photoconductive layer is excitable by a first light beam for controlling displacement by electrowetting to form a first electrode, - A first light source capable of generating said first light beam intended for the photoconductive layer of the lower substrate, - The upper substrate comprising a second electrode, - A voltage source connected to the first electrode and the second electrode so as to form an electrostatic field across said receiving space, - A device for optical analysis of the sample comprising a second excitation light source positioned above the upper substrate, capable of generating a second light beam at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - The process consisting of: - Optically treat the second light beam to cut off wavelengths likely to excite the photoconductive layer of the lower substrate.

[0013] The invention also relates to a system for optical analysis of a sample comprising a drop actuation device operating by electrowetting and capable of implementing the method defined above, said drop actuation device comprising: - A chamber formed by two substrates arranged opposite each other along a main axis, so as to form a so-called lower substrate and a so-called upper substrate, the two substrates being spaced apart from each other to form a space for receiving said sample, - The lower substrate being produced by a stack of layers in which a photoconductive layer is excitable by a first light beam for controlling displacement by electrowetting to form a first electrode, - A first light source capable of generating said first light beam intended for the photoconductive layer of the lower substrate, - The upper substrate comprising a second electrode, - A voltage source connected to the first electrode and the second electrode so as to form an electrostatic field across said receiving space, - A device for optical analysis of the sample comprising a second excitation light source positioned above the upper substrate, capable of generating a second light beam at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - The system comprising a first optical element positioned between the sample reception space and the photoconductive layer of the first substrate, - Said optical element being chosen to cut said excitation wavelength of the second light beam so that the latter does not excite the photoconductive layer.

[0014] According to a particular embodiment, the first optical element is positioned between an insulating layer of the lower substrate and the photoconductive layer.

[0015] According to another particular embodiment, the first optical element is positioned between an insulating layer of the lower substrate deposited on the photoconductive layer and the receiving space.

[0016] According to another particular embodiment, the first optical element is integrated into an insulating layer of the lower substrate deposited on the photoconductive layer.

[0017] According to another particular embodiment, the system comprises a second optical element positioned between the first light source and the receiving space, this second optical element being chosen to cut the wavelengths of the first light beam likely to overlap the wavelengths of the light emitted by the sample caused by its excitation.

[0018] Advantageously, the first optical element and the second optical element are combined in a single deposit made on the photoconductive layer of the lower substrate, this deposit also playing the role of an electrical insulating layer.

[0019] According to one feature, said deposit is produced in the form of a stack of alternating layers of TiO2 / Al2O3 or SiO2 / Al2O.

[0020] The invention also relates to a system for optical analysis of a sample comprising a drop actuation device operating by electrowetting and capable of implementing the method defined above, said drop actuation device comprising: - A chamber formed by two substrates arranged opposite each other along a main axis, so as to form a so-called lower substrate and a so-called upper substrate, the two substrates being spaced apart from each other to form a space for receiving said sample, - The lower substrate being produced by a stack of layers in which a photoconductive layer is excitable by a first light beam for controlling displacement by electrowetting to form a first electrode, - A first light source capable of generating said first light beam intended for the conductive layer of the lower substrate, - The upper substrate comprising a second electrode, - A voltage source connected to the first electrode and the second electrode so as to form an electrostatic field across said receiving space, - A device for optical analysis of the sample comprising a second excitation light source positioned above the upper substrate, capable of generating a second light beam at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - The system comprising: - A first polarizer positioned between the second light source and said reception space, this first polarizer having polarization lines oriented in a first direction, - A second optical polarizer positioned between the sample reception space and the photoconductive layer of the first substrate, this second polarizer having polarization lines oriented in a second direction orthogonal to the first direction.

[0021] According to a particular embodiment, the system also comprises a third optical polarizer positioned in front of the first light source, having polarization lines oriented along said first direction.

[0022] Advantageously, the first light source is an OLED type display. Brief description of the figures

[0023] Other characteristics and advantages will appear in the detailed description which follows, given with reference to the appended drawings in which: - [Fig.l] shows a system for optical analysis of a liquid sample and illustrates its operating principle; - [Fig.2A] shows the optical analysis system of the invention according to a first particular embodiment and [Fig.2B] illustrates the optical filtering principle used; - [Fig.3A] shows the optical analysis system of the invention according to a second particular embodiment and [Fig.3B] illustrates the optical filtering principle used; - [Fig.4A] shows the optical analysis system of the invention according to a third particular realization and [Fig.4B] illustrates the principle of optical filtering used; - [Fig.4C] shows an example of the production of a multi-layer assembly capable of providing an electrical insulation and optical filtering function; - [Fig.5] shows the optical analysis system of the invention according to a fourth particular embodiment;

[0024] In Figures 2B, 3B and 4B, a normalized optical transmission is shown as a function of the wavelength. When the high level (=1) is reached, all wavelengths are transmitted and when the low level (=0) is reached, no wavelength is transmitted.

[0025] Detailed description of at least one embodiment

[0026] In the remainder of the description, the terms "lower", "upper", "above", "below" are to be understood taking into account an axis drawn vertically in the plane of the sheet. Of course, these terms should not be considered in a limiting manner.

[0027] According to the invention, the optical analysis system comprises: - A drop actuation device operating by electrowetting; - An optical analysis device;

[0028] The system is intended for the analysis of a liquid sample.

[0029] The liquid sample is advantageously produced in the form of one or more drops 40 presented successively for analysis. The drop actuating device is controlled to move each drop 40 and fix it for optical analysis within the system.

[0030] By optical analysis, we mean for example an analysis by fluorescence or equivalent, from an image of each drop. For an analysis by fluorescence, fluorophores present in one or more drops 40 are excited using an excitation source (second light source S2) and an image of a population of drops is captured using a camera to determine the fluorescence emitted by the fluorophores after excitation.

[0031] This may of course be another type of optical analysis. The invention applies in the case where this optical analysis requires the use of a second light source S2, in addition to the light source S1 used for monitoring the movement of the drops 40 by electrowetting.

[0032] In the remainder of the description, we will consider in a non-limiting manner that the optical analysis is a fluorescence analysis.

[0033] Device for actuating drops by electrowetting

[0034] [Fig.l]

[0035] This device comprises a component having a chamber 1 defining a reception area for each 40 drop to be analyzed.

[0036] The reception space is defined by the spacing present between two substrates 100, 101 arranged in parallel.

[0037] A first substrate, called lower 101, is configured to form a first matrix of electrodes (virtual - see below). It is optionally topped with a hydrophobic layer or integrates this hydrophobic layer C50.

[0038] A second substrate, called upper 100, comprises a counter-electrode (layer C2).

[0039] The two faces of the chamber 1 facing each other are advantageously flat and parallel to each other. The lower face is designated the bottom of the chamber 1 and plays the role of the electrode matrix and the upper face integrates the counter-electrode.

[0040] A voltage source (V) connected to the first electrode and to the second electrode makes it possible to form the electrostatic fields across the system and in particular in the insulating layer C40 and the photosensitive layer C30.

[0041] As in any microfluidic system by electrowetting, the device operates by electrostatic effect and comprises means for generating several independent electrostatic fields juxtaposed between the two substrates 100, 101. The electrostatic fields are generated perpendicular to the two substrates.

[0042] According to a feature of the invention, at the level of the lower substrate, the device implements a matrix of virtual electrodes called "Opto-EWOD" as described in the publication referenced PY Chiou, H. Moon, H. Toshiyoshi, CJ Kim, and MC Wu, “Light actuation of liquid by optoelectrowetting,” Sensors Actuators, A Phys., vol. 104, no. 3, pp. 222-228, 2003.

[0043] According to this principle, the lower substrate 101 comprises a stack of layers, including a photoconductive layer C30. Light radiation L1 makes it possible to locally make the photoconductive layer C30 conductive, temporally and locally defining a virtual electrode. The light beam therefore locally induces the electrowetting effect on the scale of a droplet without having to concretely manufacture an electrode matrix. This results in a matrix of virtual electrodes.

[0044] When a virtual electrode is created under the drop 40 thanks to the optical projection of a pattern, an electrowetting effect appears, which modifies the spreading of the drop 40 by electrostatic forces, and makes it possible to trap (static virtual electrode) or move (moving virtual electrode) the drop 40.

[0045] The first light source SI may be a laser source that scans the surface of the electrowetting in order to actuate the drops on the surface, or formed from a screen-type technology, whether emissive (OLED, LED, etc.), transmissive (LCD) or projection (video projector). It is thus possible to use an OLED or equivalent type display, placed nearby under the component, capable of generating light beams LL. The layers of the lower substrate 101 located under the photoconductive layer C30 are of course transparent to the radiation emitted by this first light source SI.

[0046] [Fig.l] gives an example of a stack of layers forming the component, according to this "Opto-EWOD" principle.

[0047] The upper substrate is composed of a layer of glass C1, on which a thin layer of ITO (for Indium Tin Oxide) C2, of approximately 100nm, or another transparent conductive material, is deposited, thus forming the counter-electrode. A very thin layer C3 of a material, for example chosen to be very hydrophobic (for example PTFE for Polytetrafluoroethylene, based on polysiloxane (as described in patent application FR2887891A1) or any other hydrophobic material known to those skilled in the art of the field of electrowetting (Teflon - Registered trademark)) is then deposited. The substrate 100 is turned over to place the layer C3 downwards.

[0048] The lower substrate 101 comprises a layer of CIO glass, on which a layer of ITO C20 is deposited forming the electrode. The photoconductive layer C30 is then deposited on the ITO layer C20. An insulating layer C40 is then deposited on the photoconductive layer and then a layer C50 chosen to be hydrophobic (for example PTFE). The two substrates 100, 101 are placed opposite each other and joined from the outside to form the chamber 1 intended to receive the drops 40. The distance separating the two hydrophobic layers C3 and C50 in the height direction is chosen to be sufficient to be able to place only a single drop and not a stack, thus making it possible to be able to detect the drops of interest and to associate each drop with a single electrode of the matrix or with a group of several electrodes of the matrix.

[0049] The first light source SI is for example composed of a pixelated OLED type display, used to generate each light beam located through the lower substrate 101 and allow the activation of virtual electrodes. The size of the light beam L1 which defines a virtual electrode must preferably be less than or equal to the size of the drops.

[0050] As the principle of the invention does not necessarily work by moving the drops on a surface (as in the documents of the prior art) but by fixing the drops of interest, it is not necessarily necessary to use hydrophobic external layers C3, C50. In fact, it is possible to be satisfied with a PTFE layer (Teflon-Registered trademark) or a chemical treatment, for example with a silane such as FDTS (for Perfluorodecyltrichlorosilane).

[0051] The activation of a virtual electrode is for example carried out by a control and electrical power supply unit 2. By activating one or more pixels of the display, it makes it possible to generate a virtual electrode and to place it at an electrical potential distinct from the electrical potential of the counter-electrode (the latter electrical potential being for example zero) and thus to create a potential difference between the activated electrode and the counter electrode. Optical analysis device

[0052] [Fig.l]

[0053] To carry out an optical analysis of the drops 40 (for example by fluorescence), it is necessary to add a second excitation light source S2 conventionally placed above the component and the chamber 1 of the actuation device, to excite the sample (excitation of the fluorophores in the case of fluorescence).

[0054] This excitation light source S2 is associated with a detector D, also placed above the chamber 1, the latter being intended to capture the light signals FL1 returned by the sample after excitation. Such a configuration is standard, used in all so-called epifluorescence microscopes. It may in particular be a fluorescence imaging assembly. The excitation light source S2 emits a light beam L2 intended to excite the fluorophores present in the sample, and the detector D, for example a camera, is responsible for capturing the fluorescence FL1 emitted by the sample after excitation.

[0055] The upper substrate 100 is chosen to be transparent to the light radiation L2 emitted by the excitation light source S2 and to the fluorescence radiation FL1 emitted by the sample following excitation.

[0056] According to the invention, the cohabitation of the first light source SI dedicated to electrowetting (OLED type display for example) and the second light source S2, used to excite the sample in the context of optical analysis, is not obvious for the following two reasons: - The second light source S2 used during the optical analysis of the drops 40 must not trigger the electrowetting actuation system and cause untimely movement or trapping of the drops 40 in the chamber 1; - The detector D must only be able to detect the light emitted by each excited drop 40 and not be disturbed by the light beams emitted by the first light source SI located below and used to create the virtual electrode of the electrowetting actuation device;

[0057] These two technical problems can be solved by separate means or by a single solution, capable of handling both situations listed above.

[0058] In the first situation: - It is necessary to carry out optical filtering of the light emitted by the second light source S2 so that it does not excite the photoconductive layer C30 of the lower substrate 101 and cause disturbances in the control of the movement of the drops 40 by electrowetting;

[0059] In the second situation: - It is possible to use a suitable light source (SI), emitting over a range of wavelengths distinct from that which must be detected (for example that of fluorescence); - It is possible to set up optical filtering of the light emitted by the first light source SI so as not to disturb the optical analysis; this emitted light must not overlap the light emitted by the sample after excitation;

[0060] At a minimum, the solution of the invention must make it possible to manage the first situation, since the second situation can be managed by simply adapting the type of source used for the first light source used in the actuation device.

[0061] In the case where the first light source SI is not suitable for managing the second situation (for example, the use of a simple video projector, or a white source with a very broad emission spectrum), it is also necessary to filter the light emitted by the first light source S1 so that it does not emit in the same wavelengths as those of the light emitted by the sample, after excitation. Optical filtering - first situation

[0062] [Fig.2A]

[0063] [Fig.2B]

[0064] In the case of the first situation, the invention consists of adding an optical filter Fl between the photoconductive layer C30 and the chamber 1 receiving the sample.

[0065] As indicated above, this optical filter F1 has the function of cutting the wavelengths (denoted / ._L2) of the light beam L2 emitted by the second light source S2 which could excite the photoconductive layer C30. Thus, only the light emitted at wavelengths X_L1 by the first light source S1 (that of the OLED display) must contribute to the excitation of the photoconductive layer C30 and be able to cause the displacement of the fluorescence of a drop 40 within the actuation device.

[0066] As indicated above, the lower substrate 101 is composed of a stack of layers, including in particular the photoconductive layer C30 topped with an insulating (hydrophobic) layer.

[0067] The optical filter can thus take three different positions: - A first position, between the insulating layer C40 and the photoconductive layer C30 (as in [Fig.2A]); - A second position between the insulating layer C40 and chamber 1 occupied by the sample; - A third position, integrated into the C40 insulating layer;

[0068] As illustrated by [Fig.2B], the filter F1 is advantageously a high-pass filter, cutting the excitation wavelengths / ._L2 of the fluorescence, emitted by the second light source S2, upstream of the photoconductive layer C30. It can also be a band-stop filter, allowing all wavelengths to pass, with the exception of the wavelength / ._L2 of the source for the excitation of the fluorescence.

[0069] It can also be noted that the light emitted by the sample by fluorescence is a priori too weak to excite the photoconductive layer C30 and cause activation of the electrowetting mechanism. If this is not the case, the filter must also cut the wavelengths emitted by the sample by fluorescence. Optical filtering - second situation

[0070] [Fig.3A]

[0071] [Fig.3B]

[0072] To manage the second situation described above, a second optical filter F2 can be added.

[0073] In the second situation, it is indeed necessary to prevent the first light source SI, used for monitoring the movement of the drops 40, from emitting at the emission wavelengths of the sample, after excitation, so as not to disturb the optical analysis (for example by fluorescence) of the drops 40 at the detector D.

[0074] For this, the second optical filter F2 is added between the first light source SI and the chamber 1. In [Fig.3A], this second filter F2 is positioned between the first light source SI and the lower substrate 101.

[0075] In the simplest way, in connection with [Fig.3B], it is a question of using a band-stop filter which allows all the wavelengths (X_A allowing the activation of a virtual electrode) of the first light source SI to pass, with the exception of the wavelengths (denoted X_P1) which would overlap the wavelengths (denoted X_FL1) of the fluorescence emission of the sample and disturb the optical analysis.

[0076] Conventionally, it should be noted that a fluorescence filter is already used in front of the detector D, in order to collect only the fluorescence radiation emitted by the sample.

[0077] Optical filtering - first situation and second situation

[0078] [Fig.4A]

[0079] [Fig.4B]

[0080] [Fig.4C]

[0081] To manage the two situations set out above, it is possible to add the first filter F1 and the second filter F2 according to the arrangements proposed both in [Fig.2A] and in [Fig.3A] and with the characteristics defined above.

[0082] Furthermore, it is noted that the management of the two situations can be carried out by positioning a single filter between the photoconductive layer C30 and the chamber 1 intended to be occupied by the sample.

[0083] It is thus possible to place a single filter F3 having the following functions: - The function of cutting all wavelengths / ._L2 coming from the second light source S2, likely to excite the photoconductive layer C30, and - The function of cutting the wavelengths / .PI coming from the first light source SI, likely to overlap with the wavelengths / .FL I of fluorescence emitted by the sample after excitation.

[0084] This can be a two-way high-pass filter, with a cutoff above the fluorescence wavelength / .FL I or a wider notch filter ( [Fig.4B]).

[0085] According to an advantageous embodiment, a single deposit is made on the photoconductive layer, this playing both the role of filter F3 and that of the insulation layer (C40).

[0086] For example, as illustrated by [Fig.4C], this deposit can be a stack of alternating layers of TiO2 / Al2O3 or SiO2 / Al2O3. Optical polarization

[0087] To manage the first situation set out above, it is also possible to use the principle of optical polarization of the light beam L2 emitted by the second light source S2.

[0088] An optical polarizer typically has several polarization lines oriented in parallel. This is a component that will only allow the component of the optical signal to pass through having a polarization direction parallel to the axis of the polarizer.

[0089] This then involves adding a first polarizer PI to linearly polarize, in a first direction, the light beam L2 generated by the second light source S2 (for excitation) and placing between the photoconductive layer C30 and the chamber 1 a second polarizer P2, in a direction orthogonal to the first direction, that is to say that the polarization axis of the second polarizer is orthogonal to the axis of the first polarizer, and consequently the light which has passed through the first polarizer will be blocked by the second polarizer. Thus in this configuration, the light coming from the second light source S2 does not reach the photoconductive layer C30 and is therefore not absorbed by it.

[0090] In connection with [Fig.5], to manage the two situations set out above, a third polarizer P3 is added to the polarizers PI, P2 already present in front of the first light source SI, the axis of the polarizer P3 being oriented in the first direction (the same as the first polarizer PI). In this configuration, the light from the second light source S2 does not reach the photoconductive layer C30 and is therefore not absorbed by it, and the light from the first light source SI for actuation does not reach the sample, and therefore is not detected on the fluorescence detection path. Layer structuring

[0091] In another variant embodiment, in order to manage the two situations set out above, it would also be possible to provide a structuring of the surface of the insulating layer located above the photoconductive layer.

[0092] This structuring, having controlled diffraction or refraction properties, will make it possible to change the direction of the radiation. Thus the light emitted by the second light source S2 will be deflected and will not be able to reach the photoconductive layer C30, and the light emitted by the first light source S1 will not be able to reach the detector D.

[0093] This structuring could, for example, create networks or metasurfaces.

[0094] The invention thus presents numerous advantages, among which: - It allows to simply resolve conflicts between the light sources of such an optical analysis system; - The various solutions proposed are easy to implement in an existing system and do not require any specific programming, as in the state of the art; - The proposed solutions use readily available and inexpensive means;

Claims

Claims

1. Method for optical analysis of a sample in a drop actuation device operating by electrowetting, said actuation device comprising: - A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a main axis, so as to form a so-called lower substrate (101) and a so-called upper substrate (100), the two substrates being spaced apart from each other to form a space for receiving said sample, - The lower substrate being produced by a stack of layers in which a photoconductive layer (C30) is excitable by a first light beam (L1) for controlling movement by electrowetting to form a first electrode, - A first light source (SI) capable of generating said first light beam (L1) intended for the photoconductive layer (C30) of the lower substrate (101), - The upper substrate (100) comprising a second electrode,- A voltage source (V) connected to the first electrode and to the second electrode so as to form an electrostatic field across said receiving space, - A device for optical analysis of the sample comprising a second excitation light source (S2) positioned above the upper substrate (100), capable of generating a second light beam (L2) at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate (100) caused by its excitation, - Characterized in that the method consists of: - Optically treating the second light beam (L2) to cut the wavelengths (X_L2) capable of exciting the photoconductive layer (C30) of the lower substrate.,

2. System for optical analysis of a sample comprising a drop actuation device operating by electrowetting and capable of implementing the method defined in claim 1, said drop actuating device comprising: - A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a main axis, so as to form a so-called lower substrate (101) and a so-called upper substrate (100), the two substrates being spaced apart from each other to form a space for receiving said sample, - The lower substrate (101) being produced by a stack of layers in which a photoconductive layer (C30) is excitable by a first light beam (L1) for controlling displacement by electrowetting to form a first electrode, - A first light source (SI) capable of generating said first light beam (Ll) intended for the photoconductive layer (C30) of the lower substrate, - The upper substrate (100) comprising a second electrode, - A voltage source (V) connected to the first electrode and to the second electrode so as to form an electrostatic field across said receiving space, - A device for optical analysis of the sample comprising a second excitation light source (S2) positioned above the upper substrate (100), capable of generating a second light beam (L2) at an excitation wavelength (X_L2), and a unit for detecting the light emitted by said sample through said upper substrate (100) caused by its excitation, - Characterized in that: - The system comprises a first optical element (Fl) positioned between the sample reception space and the photoconductive layer (C30) of the first substrate, - Said optical element being chosen to cut said excitation wavelength (X_L2) of the second light beam (L2) so that the latter does not excite the photoconductive layer (C30).

3. System according to claim 2, characterized in that the first optical element is positioned between an insulating layer (C40) of the lower substrate (101) and the photoconductive layer (C30).

4. System according to claim 2, characterized in that the first optical element is positioned between an insulating layer (C40) of the lower substrate (101) deposited on the photoconductive layer (C30) and the reception space.

5. System according to claim 2, characterized in that the first optical element is integrated in an insulating layer (C40) of the lower substrate (101) deposited on the photoconductive layer (C30).

6. System according to claim 2, characterized in that it comprises a second optical element (F2) positioned between the first light source (SI) and the reception space, this second optical element being chosen to cut the wavelengths (X_P1) of the first light beam (Ll) likely to overlap the wavelengths ( / .FL 1 ) of the light emitted by the sample caused by its excitation.

7. System according to claim 6, characterized in that the first optical element (F1) and the second optical element (F2) are combined in a single deposit made on the photoconductive layer (C30) of the lower substrate (101), this deposit also playing the role of an electrical insulating layer (C40).

8. System according to claim 7, characterized in that said deposit is produced in the form of a stack of alternating layers of TiO2 / Al2O3 or SiO2 / Al2O.

9. System for optical analysis of a sample comprising a drop actuation device operating by electrowetting and capable of implementing the method defined in claim 1, said drop actuation device comprising: - A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a main axis, so as to form a so-called lower substrate (101) and a so-called upper substrate (100), the two substrates being spaced apart from each other to form a space for receiving said sample, - The lower substrate (101) being produced by a stack of layers in which a photoconductive layer (C30) is excitable by a first light beam (L1) for controlling movement by electrowetting to form a first electrode, - A first light source (SI) capable of generating said first light beam (L1) to the conductive layer of the lower substrate, - The upper substrate (100) comprising a second electrode, - A voltage source (V) connected to the first electrode and to the second electrode so as to form an electrostatic field across said receiving space, - A device for optical analysis of the sample comprising a second excitation light source (S2) positioned above the upper substrate, capable of generating a second light beam (L2) at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - Characterized in that the system comprises: - A first polarizer (PI) positioned between the second light source (S2) and said receiving space,this first polarizer having polarization lines oriented in a first direction, - A second optical polarizer (P2) positioned between the sample reception space and the photoconductive layer (C30) of the first substrate, this second polarizer having polarization lines oriented in a second direction orthogonal to the first direction.,

10. System according to claim 9, characterized in that it comprises a third optical polarizer (P3) positioned in front of the first light source (SI), having polarization lines oriented in said first direction.

11. System according to one of claims 2 to 10, characterized in that the first light source (SI) is an OLED type display.

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